Rob. L. Evans, Greg Hirth, Kiyoshi Baba, Don Forsyth, Alan Chave & Randall Mackie, Geophysical evidence from the MELT area for
compositional controls on oceanic plates, Nature, 8 Sept 2005
Magnetotelluric and seismic data, collected during the MELT
experiment at the southern East Pacific Rise, constrain the
distribution of melt beneath this mid-ocean-ridge spreading
centre and also the evolution of the oceanic lithosphere during its early cooling history. Here we focus on structures imaged at distances,100 to 350km east of the ridge crest, corresponding to seafloor ages of ,1.3 to 4.5 million years (Myr), where the seismic and electrical conductivity structure is nearly constant and
independent of age. Beginning at a depth of about 60 km, we image a large increase in electrical conductivity and a change from isotropic to transversely anisotropic electrical structure, with higher conductivity in the direction of fast propagation for seismic waves. Conductive cooling models predict structure that increases in depth with age, extending to about 30km at 4.5Myr
ago.We infer, however, that the structure of young oceanic plates is
instead controlled by a decrease in water content above a depth of
60 km induced by the melting process beneath the spreading
centre |
